The specific aims of this research are to: 1) increase knowledge of regulation of branched-chain amino acid (BCAA) and branched-chain Alpha-ketoacid (BCKA) metabolism; 2) to determine how dietary and endocrine treatments of animals influence the activities of BCAA aminotransferase (BCAA-T) and BCKA dehydrogenase (BCKA-D) in different tissues and metabolism of BCAA and BCKA in isolated organ systems and in vivo in the rat; 3) to establish the basis for the leucine: isoleucine and valine (leu:ile and val) antagonism observed with animals fed high leu diets; and 4) to enlarge knowledge of interorgan relationships in BCAA metabolism. One series of experiments will be done with isolated kidney mitochondria to study factors affecting the catabolism of L[14C] val to Alpha-ketoisocaproic acid (KIV) and oxidation of KIV at carbon-1 to yield CO2. Variables to be examined include concentrations of amino acids in the medium, the integrity of the mitochondrial membrane, the level of BCAA-T and the level and degree of activation of BCKA-D. Another series will involve measurements of BCAA-T activity in both mitochondria and cytosol and of unactivated and activated BCKA-D in mitochondria of rats fed diets differing in protein content and in the quantities of BCAA they contain, or treated with insulin, glucagon, epinephrine or cortisol. Measurements will also be made of BCAA oxidation in vivo using L[14C]leu as a tracer in rats treated in various of these ways. In a third series of experiments, effects on enzymes of BCAA catabolism, and on ile and val metabolism in vivo, of feeding rats excess leu will be studied. Blood and tissue BCAA and BCKA will be measured and relationships between changes in brain amino acid concentrations and food intake will be examined. The long-term objective is to enlarge the base of knowledge about branched-chain amino acid metabolism in the intact organism in relation to conditions in which altered metabolism of these amino acids may have clinical implications. These include liver failure, trauma, renal disease and urea cycle defects, diabetes and long-term fasting or starvation.